This invention relates generally to X-ray inspection systems and more particularly to collimators for such systems.
It is known to use linear detectors with X-ray inspection systems for industrial parts. Linear detectors can provide improved contrast resolution and are thus well suited for digital radiography (DR) and computed tomography (CT). Improved contrast resolution is achieved by the use of x-ray collimation, which reduces the contribution of scattered X-rays to the resulting image. Ideally, the x-ray detector is horizontally collimated to provide rejection of in-plane scatter. This horizontal collimation generally takes the form of an array of tungsten plates radially aligned about the x-ray focal spot, placed in front of the x-ray detector elements. This presents a horizontal aperture for each detector element. The precision and uniformity of this structure strongly affects image quality. Large collimation arrays (in both length and depth) are required to inspect large or dense parts. Because of the limitations of prior art manufacturing and assembly methods, the difficulty of construction and hence the cost of high precision, high uniformity collimation arrays increases as the physical size of the array increases.
Accordingly, there is a need for a collimator for high energy X-ray inspection systems that can be readily manufactured at any size, while preserving precision and uniformity and minimizing complexity and cost.
The above-mentioned need is met by the present invention, which provides in one aspect a collimator comprising a carrier having a planar top surface; an arcuate base disposed on the carrier, comprising at least one arcuate bar section made from a radio-opaque material. The bar sections include a plurality of parallel grooves formed in inner and outer edges thereof. A plurality of radio-opaque collimator plates are disposed on the arcuate base in a radial array with a bottom edge of each collimator plate in contact with the top surface of the arcuate base. First and second alignment tabs extend downward from the bottom edges of the collimator plates and engage the grooves formed in the edges of the bar sections.
In another aspect, the present invention provides a method for assembling a collimator including the steps of: providing a carrier having a planar top surface; providing an arcuate base disposed on the top surface of the carrier, the arcuate base comprising one or more arcuate bar sections having a plurality of parallel grooves formed in inner and outer edges thereof; providing a plurality of radio-opaque collimator plates, each of said plates being generally rectangular and having first and second alignment tabs extending downward from a bottom edge thereof; disposing the collimator plates on the arcuate base with the alignment tabs fitting into the grooves in the arcuate base, such that the collimator plates are positioned in a radial array with respect to said arcuate base, and the bottom edge of each collimator plate is in contact with the top surface of the arcuate base; aligning the collimator plates perpendicular to the top surface of the arcuate base; and securing the collimator plates thereto.
In yet another aspect of the present invention, an alignment fixture is provided for assembling a collimator having a radial array of plates disposed on an arcuate base. The alignment fixture includes a body having a plurality of ribs formed on its bottom surface for engaging the array of collimator plates. The ribs are arranged in a radial pattern corresponding to a desired arrangement of the collimator plates. The alignment fixture includes means for positioning the alignment fixture in a circumferential direction with respect to said arcuate base.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.